1. Field of the Invention
The present invention relates generally to methods and apparatus for making plastic lenses using ultraviolet light.
2. Description of Related Art
It is conventional in the art to produce optical lenses by thermal curing techniques from the polymer of diethylene glycol bis(allyl)-carbonate (DEG-BAC). In addition, optical lenses may also be made using ultraviolet (xe2x80x9cUVxe2x80x9d) light curing techniques. See, for example, U.S. Pat. No. 4,728,469 to Lipscomb et al., U.S. Pat. No. 4,879,318 to Lipscomb et al., U.S. Pat. No. 5,364,256 to Lipscomb et al., U.S. Pat. No. 5,415,816 to Buazza et al., U.S. Pat. No. 5,529,728 to Buazza et al., U.S. Pat. No. 5,514,214 to Joel et al., and U.S. patent application Ser. No. 07/425,371 filed Oct. 26, 1989, Ser. No. 08/454,523 filed May 30, 1995, Ser. No. 08/453,770 filed May 30, 1995, Ser. No. 07/932,812 filed Aug. 18, 1992, Ser. No. 08/636,510 filed Apr. 19, 1996, all of which are hereby specifically incorporated hereby by reference.
Curing of a lens by ultraviolet light tends to present certain problems that must be overcome to produce a viable lens. Such problems include yellowing of the lens, cracking of the lens or mold, optical distortions in the lens, and premature release of the lens from the mold. In addition, many of the useful UV-curable lens forming compositions exhibit certain characteristics which increase the difficulty of a lens curing process. For example, due to the relatively rapid nature of ultraviolet light initiated reactions, it is a challenge to provide a composition which is UV curable to form an eyeglass lens. Excessive exothermic heat tends to cause defects in the cured lens. To avoid such defects, the level of photoinitiator may be reduced to levels below what is customarily employed in the ultraviolet curing art.
While reducing the level of photoinitiator addresses some problems, it may also cause others. For instance, lowered levels of photoinitiator may cause the material in regions near an edge of the lens and proximate a gasket wall in a mold cavity to incompletely cure due to the presence of oxygen in these regions (oxygen is believed to inhibit curing of many lens forming compositions or materials). Uncured lens forming composition tends to result in lenses with xe2x80x9cwetxe2x80x9d edges covered by sticky uncured lens forming composition. Furthermore, uncured lens forming composition may migrate to and contaminate the optical surfaces of the lens upon demolding. The contaminated lens is then often unusable.
Uncured lens forming composition has been addressed by a variety of methods (see, e.g., the methods described in U.S. Pat. No. 5,529,728 to Buazza et al). Such methods may include removing the gasket and applying either an oxygen barrier or a photoinitiator enriched liquid to the exposed edge of the lens, and then re-irradiating the lens with a dosage of ultraviolet light sufficient to completely dry the edge of the lens prior to demolding. During such irradiation, however, higher than desirable levels of irradiation, or longer than desirable periods of irradiation, may be required. The additional ultraviolet irradiation may in some circumstances cause defects such as yellowing in the lens.
The low photoinitiator levels utilized in many ultraviolet curable lens forming compositions may produce a lens which, while fully-cured as measured by percentage of remaining double bonds, may not possess sufficient crosslink density on the lens surface to provide desirable dye absorption characteristics during the tinting process.
Various methods of increasing the surface density of such UV curable lenses are described in U.S. Pat. No. 5,529,728 to Buazza et al. In one method, the lens is demolded and then the surfaces of the lens are exposed directly to ultraviolet light. The relatively short wavelengths (around 254 nm) provided by some UV sources (e.g., a mercury vapor lamp) tend to cause the material to crosslink quite rapidly. An undesirable effect of this method, however, is that the lens tends to yellow as a result of such exposure.
Another method involves exposing the lens to relatively short wavelengths while it is still within a mold cavity formed between glass molds. The glass molds tend to absorb the more effective short wavelengths, while transmitting wavelengths of about 365 nm. This method generally requires long exposure times and often the infrared radiation absorbed by the lens mold assembly will cause premature release of the lens from a mold member. The lens mold assembly may be heated prior to exposure to high intensity ultraviolet light, thereby reducing the amount of radiation necessary to attain a desired level of crosslink density. This method, however, is also associated with a higher rate of premature release.
It is well known in the art that a lens mold/gasket assembly may be heated to cure the lens forming composition from a liquid monomer to a solid polymer. It is also well known that such a lens may be thermally postcured by applying convective heat to the lens after the molds and gaskets have been removed from the lens.
In this application the terms xe2x80x9clens forming materialxe2x80x9d and xe2x80x9clens forming compositionsxe2x80x9d are used interchangeably.
One aspect of the invention relates to applying an oxygen barrier around the exposed edges of a lens to initiate the reaction of incompletely cured lens forming material proximate the lens edges. In an embodiment, a liquid polymerizable lens forming composition is placed in a mold cavity having at least two molds and/or a gasket. Ultraviolet rays may be directed toward at least one of the mold members to substantially cure the lens forming composition to a lens having material proximate the edges of the lens that is not fully cured. The gasket may be removed to expose the edges of the lens, and an oxygen barrier comprising a photoinitiator may be placed around the exposed edges of the lens such that at least a portion of the oxygen barrier photoinitiator is proximate lens forming composition that is not fully cured. A portion of the incompletely cured material may be removed manually prior to the application of the oxygen barrier. Subsequently another set of ultraviolet rays may be directed towards the lens such that at least a portion of the oxygen barrier photoinitiator initiates reaction of lens forming composition while the oxygen barrier substantially prevents oxygen from outside the oxygen barrier from contacting at least a portion of the lens forming composition. The lens may be allowed to cool and the oxygen barrier may be removed. The lens may be tinted after the cure is completed.
The oxygen barrier may include a flexible, stretchable, self-sealing film that is at least partially transparent to ultraviolet rays. The oxygen barrier may include polyethylene impregnated with a photoinitiator. The film may include a strip of high density polyethylene that is about 0.01-1.0 mm thick, and more preferably about 0.01-0.10 mm thick. Thicker films tend to be less conformable and stretchable. The oxygen barrier may include a plastic film that is less than about 0.025 mm thick. (e.g., about 0.0127 mm thick) and that was made by (a) immersing or running a plastic film in or through a solution comprising a photoinitiator and an etching agent (b) removing the plastic film from the solution, and (c) drying the plastic film. A surface on the plastic film may be chemically etched prior to or while immersing the plastic film in the solution.
Another aspect of the invention relates to applying conductive heat to the face of a lens. In an embodiment of the invention, a liquid polymerizable lens forming composition is placed in a mold cavity having a first mold member and a second mold member. First ultraviolet rays may be directed toward at least one of the mold members to cure the lens forming composition to a lens. A mold member may be applied to a substantially solid conductive heat source. Heat may be conductively applied to a face of the lens by (a) conductively transferring heat to a face of a mold member from the conductive heat source, and (b) conductively transferring heat through such mold member to the face of the lens.
In an embodiment, a flexible heat distributor may be placed between the heat source and the mold member to partially insulate the mold member and to slowly and uniformly transfer heat to the face of the mold member. The distributor may be shaped to conform to the face of a mold member. The heat source may include a concave element that may conform to the convex face of a mold member. The heat source may include a convex element that may conform to the concave face of a mold member. The temperature of the heat source may be thermostatically controlled. Heat may be conductively applied through a mold member to the back face of the lens, thereby enhancing the cross-linking and tintability of the lens forming material proximate to the surface of the back face of the lens (e.g., when an untintable scratch resistant coating is on the front face of the lens).
In an embodiment of the invention an eyeglass lens may be formed by (a) placing a liquid, polymerizable lens-forming composition in a mold cavity defined by at least a first mold member and a second mold member, (b) applying a plurality of preferably high intensity ultraviolet light pulses to the lens forming composition, at least one of the pulses having a duration of less than about one second (more preferably less than about 0.1 seconds. and more preferably between 0.1 and 0.001 seconds), and (c) curing the lens forming composition to form a substantially clear eyeglass lens in a time period of less than 30 minutes (more preferably less than 20 minutes, and more preferably still less than 15 minutes).
The pulses preferably have a sufficiently high intensity such that reaction is initiated in substantially all of the lens forming composition that is exposed to pulses in the mold cavity. In one embodiment reaction is initiated in substantially all of any cross section of the lens forming composition that is exposed to pulses in the mold cavity. Preferably the temperature begins to rise after such application of UV light.
The lens forming composition may be exposed to UV light from one, two, or multiple sources. Two sources may be applied on opposite sides of the mold cavity to apply light to the lens forming composition from two sides. In an alternate embodiment, the lens forming composition is exposed to a relatively low intensity ultraviolet light before or while the pulses are applied. Such pulses are preferably relatively high in intensity, and are preferably applied to the other side of the mold cavity than the relatively low intensity light.
The lens forming composition is preferably exposed to a relatively low intensity ultraviolet light while the pulses are applied, the relatively low intensity light having an intensity of less than 0.01 watt/cm2 (and more preferably less than 0.001 watt/cm2, and more preferably still 2-30 milliwatts/cm2), as measured on an outside surface of a mold member of the mold cavity. The relatively low intensity light tends to provide a low amount of light to keep the reaction going in a more steady or even manner between pulses.
Preferably at least one or even all of the pulses has an intensity of at least 0.01 watt/cm2, as measured on an outside surface of a mold member of the mold cavity. Alternately at least one or even all of the pulses have an intensity of at least 0.1 or 1 watt/cm2.
Sufficient ultraviolet light can be applied such that the temperature of the lens forming composition begins to increase. Then in one embodiment at least 5 minutes of waiting or darkness occurs before applying additional light (e.g., pulses). The waiting or darkness allows heat to dissipate, thus tending to prevent excessive heat buildup in the mold cavity. In one embodiment at least 5, 10, or 20 pulses are applied to the lens forming composition before waiting for about 5-8 minutes and then additional light is applied.
The eyeglass lens has an average thickness of at least about 1.5-2.0 mm. Thicker lenses tend to be more difficult to cure with continuous non-pulsed light.
The mold cavity is preferably cooled with air or cooled air. One significant advantage of light pulses is that ambient air may be used to cool the mold cavity, instead of cooled air. Thus significant lens curing costs may be avoided since air coolers tend to be costly to purchase and operate.
The pulses preferably emanate from a flash source of light (i.e., xe2x80x9ca flash lightxe2x80x9d) such as a xenon light source. Preferably pulses are applied such that the lens forming composition is oversaturated with ultraviolet light during at least one pulse. Flash lights are advantageous in that they have a short xe2x80x9cwarm-upxe2x80x9d time (as opposed to continuous lights that tend to require 5-60 minutes to stabilize).
Lenses may be formed with pulsed light that have more difficult to case prescriptions such as lenses with a power greater than positive 2 diopters, or lenses with a power less than minus 4 diopters.
One advantage of pulsed light application via flash lights is that even though higher intensities of light are applied, because the duration of the pulses is so short the total amount of light energy applied to cure the lens forming composition is lessened. Thus less radiant heat is applied to the mold cavity, thereby reducing cooling requirements. Moreover, energy is saved. In one embodiment less than 20, 10, 5, or 1 Joule/cm2 of energy is applied to cure the lens forming composition into a lens.
Preferably the ultraviolet light is applied as a function of the temperature of the lens forming composition, as measured directly or indirectly by measuring a temperature within the chamber (e.g., a temperature of at least a portion of the mold cavity) or by measuring a temperature of air in or exiting the chamber.
In another embodiment of the invention, an eyeglass lens may be cured by (a) placing a liquid, polymerizable lens forming composition in a mold cavity defined by at least a first mold member and a second mold member, the lens forming composition comprising a photoinitiator, (b) applying ultraviolet light at an intensity to the lens forming composition through at least one of the mold members for a selected period of time such that a temperature of the composition begins to increase, (c) decreasing the intensity of the ultraviolet light to inhibit the temperature of the lens forming composition from increasing to a selected first temperature, (d) alloying an exothermic reaction of the lens forming composition to increase the temperature of the lens forming composition to a second temperature, the second temperature being less than the selected first temperature, (e) curing the lens forming composition to form a substantially clear eyeglass lens by: (i) applying ultraviolet light at an intensity to the lens forming composition through at least one of the mold members, and (ii) decreasing the intensity of the ultraviolet light; and (f) wherein the eyeglass lens is formed from the lens forming composition in a time period of less than about 30 minutes.
In another embodiment of the invention an eyeglass lens may be made by (a) placing a liquid, polymerizable lens-forming composition in a mold cavity defined by at least a first mold member and a second mold member, the lens forming composition comprising a photoinitiator, (b) applying first ultraviolet light to at least one of the mold members for a selected first period of time such that a temperature of the lens forming composition begins to increase, (c) removing the first ultraviolet light from at least one of the mold members, thereby inhibiting the temperature of the composition from increasing to a selected first temperature, (d) repeatedly and alternately performing the following steps to complete the formation of a lens: (i) applying second ultraviolet light to at least one of the mold members for a selected second period of time and (ii) removing the second ultraviolet light from at least one of the mold members for a selected third period of time.
In an alternate embodiment of the invention an eyeglass lens may be made by (a) placing a liquid, polymerizable lens forming composition in a mold cavity defined by at least a first mold member and a second mold member, the lens forming composition comprising a photoinitiator, (b) directing ultraviolet light at a first intensity toward at least one of the mold members for a selected first period of time such that a temperature of the composition begins to increase, (c) decreasing the first intensity of ultraviolet light from at least one of the mold members, (d) repeatedly directing a plurality of pulses of ultraviolet to the lens forming composition through at least one of the mold members to complete formation of a substantially clear eyeglass lens, at least one of the pulses lasting for a second period of time, and wherein a third period of time exists between application of at least two of the pulses.
An apparatus of the invention may include: (a) a first mold member having a casting face and a non-casting face. (b) a second mold member having a casting face and a non-casting face, the second mold member being spaced apart from the first mold member during use such that the casting faces of the first mold member and the second mold member at least partially define a mold cavity, (c) a first pulse light generator adapted to generate and direct a pulse of ultraviolet light toward at least one of the first and second mold members during use, and (d) a controller adapted to control the first pulse light generator such that ultraviolet light is directed in a plurality of pulses toward at least one of the first and second mold members, at least one of the pulses having a duration of less than one second.
A system of the invention may include (a) a lens forming composition comprising a photoinitiator, (b) a first mold member having a casting face and a non-casting face, (c) a second mold member having a casting face and a non-casting face, the second mold member being spaced apart from the first mold member during use such that the casting faces of the first mold member and the second mold member at least partially define a mold cavity for the lens forming composition, (d) a first pulse light generator adapted to generate and direct a pulse of ultraviolet light toward at least one of the first and second mold members during use, (e) a controller adapted to control the first pulse light generator such that ultraviolet light is directed in a plurality of pulses toward at least one of the first and second mold members, at least one of the pulses having a duration of less than one second, and (f) wherein the system is adapted to cure the lens forming composition to form a substantially clear eyeglass lens in less than 30 minutes.
The lens forming composition preferably comprises at least one polyethylenic-functional monomer containing at least two ethylenically unsaturated groups selected from acrylyl and methacrylyl, at least one polyethylenic-functional monomer containing at least three ethylenically unsaturated groups selected from acrylyl and methacrvlyl, and/or an aromatic containing bis(allyl carbonate)-functional monomer.
A system of the invention may include: (a) a lens forming composition comprising a photoinitiator, (b) a mold cavity chamber comprising a first mold member having a casting face and a non-casting face, a second mold member having a casting face and a non-casting face, the second mold member being spaced apart from the first mold member during use such that the casting faces of the first mold member and the second mold member at least partially define a mold cavity for the lens forming composition, (c) a first light generator adapted to generate and direct a ultraviolet light in a first intensity toward at least one of the first and second mold members during use, (d) a temperature sensor adapted to sense a temperature in the chamber or a temperature of air exiting the chamber, (e) a controller coupled to the temperature sensor and adapted to control the first light generator such that the first intensity of ultraviolet light directed toward at least one of the first and second mold members is decreased when a temperature measured by the temperature sensor substantially increases, and (f) wherein the system is adapted to cure the lens forming composition to form a substantially clear eyeglass lens in less than 30 minutes.
An apparatus of the invention may include (a) a first mold member having a casting face and a non-casting face, (b) a second mold member having a casting face and a non-casting face, the second mold member being spaced apart from the first mold member during use such that the casting faces of the first mold member and the second mold member at least partially define a mold cavity for a lens forming composition, (c) an ultraviolet light generator adapted to generate and direct ultraviolet light toward at least one of the first and second mold members during use, (e) a controller for controlling the intensity of light directed by the light generator, (f) a light sensor adapted to measure the intensity of light directed by the ultraviolet light generator, the light sensor being adapted to signal the light generator to vary the intensity of the ultraviolet light being produced, and (g) a filter adapted to inhibit light other than ultraviolet light from impinging upon the light sensor.
In an alternate embodiment, a system for making an eyeglass lens may include (a) a first mold member having a casting face and a non-casting face, (b) a second mold member having a casting face and a non-casting face, the second mold member being spaced apart from the first mold member during use such that the casting faces of the first mold member and the second mold member at least partially define a mold cavity for a lens forming composition, (c) an ultraviolet light generator adapted to generate and direct ultraviolet light toward at least one of the first and second mold members during use, (d) a distributor adapted to direct air toward the non-casting face of at least one of the mold members, (e) a thermoelectric cooling system adapted to cool the air, and (f) a first blower adapted to receive effluent air that has contacted the non-casting face of the mold member and to recycle the effluent air to the distributor.
In an embodiment, an eveglass lens may be made by (a) placing a liquid, polymerizable lens forming composition in a mold cavity defined at least partially by a first mold member and a second mold member, the lens forming composition comprising a photoinitiator; (b) directing a plurality of pulses of ultraviolet light toward the lens forming composition through at least one of the mold members to initiate reaction of the lens forming composition, at least one of the pulses having an intensity of at least about 10 milliwatts/cm2; (c) subsequent to the step of directing the plurality of pulses toward the lens forming composition, directing ultraviolet light of a second intensity toward the lens forming composition through at least one of the mold members to form a substantially clear eyeglass lens, the second intensity being less than about 350 microwatts/cm2; and (d) substantially simultaneously with the step of directing ultraviolet of a second intensity toward the lens forming composition, directing air onto a non-casting face of at least one of the mold members to remove heat from the lens forming composition.
A lens having a scratch resistant coating may be formed by: placing a first coating composition within a mold member, the mold member comprising a casting face and a non-casting face, the coating composition comprising a photoinitiator and being curable upon exposure to ultraviolet light; (a) placing a first coating composition within a mold member, the mold member comprising a casting face and a non-casting face, the coating composition comprising a photoinitiator and being curable upon exposure to ultraviolet light; (b) spinning the mold member to distribute the first coating composition over the casting face; (c) directing ultraviolet light at the mold member to cure at least a portion of the first coating composition; (d) placing a second coating composition within the mold member, the second coating composition comprising a photoinitiator and being curable upon exposure to ultraviolet light; (e) spinning the mold member to distribute the second coating composition over the portion of the first coating composition that has been cured; (f) directing ultraviolet light at the mold member, thereby curing at least a portion of the second coating composition and forming a substantially clear combination coat comprising at least a portion of each of the first and second coating compositions; (g) assembling the mold member with a second mold member to form a mold having a cavity between the mold members; (h) placing a lens-forming composition within the cavity, the lens-forming composition comprising a photoinitiator and being curable upon exposure to ultraviolet light; and (i) directing ultraviolet light at the mold to cure at least a portion of the lens-forming material to form a lens, and wherein the combination coat adheres to the cured portion of the lens-forming material.